There have heretofore been known longitudinal electric field types of liquid crystal devices, which are provided with a liquid crystal cell as a basic constitution. The liquid crystal cell comprises a pair of base plates with electrodes, which base plates with electrodes are located so as to stand facing each other, and a liquid crystal layer supported between the pair of the base plates with electrodes. With the longitudinal electric field types of the liquid crystal devices, orientation of liquid crystal molecules contained in the liquid crystal layer is altered between the time free from voltage application across the liquid crystal layer and the time of voltage application across the liquid crystal layer, and displaying operations, or the like, are thereby performed. With the liquid crystal devices described above, an orientating film is located on each of inside surfaces of the pair of the base plates with electrodes, and the orientation (i.e., a pre-tilt angle and a twist angle) of the liquid crystal molecules at the time free from voltage application is regulated by the orientating films. Also, at the time of voltage application, the orientation of the liquid crystal molecules is altered along the electric field direction (in the cases of the longitudinal electric field types of the liquid crystal devices, along the direction normal to the orientating films). In a twisted nematic (TN) mode, the twist angle at the time free from voltage application is equal to 90°.
In the cases of the liquid crystal devices described above, a polarizer is located on the side outward from the liquid crystal cell, and light is irradiated via the polarizer to the liquid crystal layer. The light having entered into the liquid crystal layer is radiated out via the polarizer to the side of a person, who views the displayed image.
In the cases of transmission types of liquid crystal devices, a pair of polarizers are located respectively on opposite sides outward from a combination of a pair of base plates constituting a liquid crystal cell (i.e., on the light incidence side and the light radiating side). The combination of the pair of the polarizers are selected such that the light may not be radiated out to the side of the person, who views the displayed image, in an orientated state of the liquid crystal molecules at the time free from voltage application or at the time of voltage application. Specifically, in the TN mode, in cases where the pair of the polarizers are located in accordance with a crossed Nicols arrangement, in which the axes of polarization of the pair of the polarizers are normal to each other, the operation mode is set in a normally white mode, in which the liquid crystal devices are set in a bright state at the time free from voltage application. Also, in cases where the pair of the polarizers are located in accordance with a parallel Nicols arrangement, in which the axes of polarization of the pair of the polarizers are parallel with each other, the operation mode is set in a normally black mode, in which the liquid crystal devices are set in a bright state at the time of voltage application.
Besides the polarizers, the liquid crystal devices are provided with phase difference compensation elements. Functions of the phase difference compensation elements will be described hereinbelow by taking the normally white TN mode, in which the liquid crystal devices are set in a dark state at the time of voltage application, as an example.
In the normally white TN mode, in cases where the liquid crystal devices are not provided with the phase difference compensation elements, at the time of voltage application, at which the liquid crystal molecules are set in an approximately normal orientated state (i.e., in an approximately uniaxial orientated state), the liquid crystal layer exhibits little birefringent characteristics with respect to normal incident light and directly transmits linearly polarized light, which has impinged upon the liquid crystal layer from the direction normal to the liquid crystal layer. However, in such cases, the liquid crystal layer exhibits the birefringent characteristics with respect to oblique incident light, and therefore the linearly polarized light, which has impinged upon the liquid crystal layer from an oblique direction, is converted into elliptically polarized light, and the elliptically polarized light having thus been produced is radiated out from the liquid crystal layer. Part of the elliptically polarized light, which has thus been radiated out from the liquid crystal layer, passes through the polarizer, which is located on the light radiating side of the liquid crystal device. As a result, the degree of darkness becomes low. Specifically, the contrast becomes low. Also, in cases where the incidence angle of the oblique incident light upon the liquid crystal layer becomes large, the birefringent characteristics become high, and the degree of lowering of the contrast becomes high. Therefore, the angle of field, at which a high contrast is capable of being obtained, becomes narrow. Accordingly, phase difference compensation elements are utilized, which have a phase difference compensating function (A) for compensating for a phase difference of the aforesaid elliptically polarized light occurring due to the birefringence of the oblique incident light, and for restoring the elliptically polarized light to the linearly polarized light.
Further, in the normally white TN mode, at the time of voltage application, the liquid crystal molecules contained in the liquid crystal layer are set in the approximately normal orientated state as a whole. However, the liquid crystal molecules, which are located in the vicinity of each of the orientating films, are affected by the orientating film. Therefore, it often occurs that the liquid crystal molecules, which are located in the vicinity of each of the orientating films, are set in a hybrid orientated state, in which the direction of the orientation of the liquid crystal molecules is altered successively from the approximately normal direction to the direction of the orientation of each of the orientating films. Accordingly, the phase difference compensation elements should preferably have, besides the aforesaid phase difference compensating function (A), a phase difference compensating function (B) with respect to the birefringence due to the liquid crystal molecules having been set in the hybrid orientated state.
Recently, phase difference compensation elements constituted of inorganic materials have been proposed. The phase difference compensation elements constituted of the inorganic materials have a high heat resistance, a high light resistance, good chemical stability, and the like, and are appropriate for use in, for example, liquid crystal devices to be loaded in projection type display apparatuses, such as projectors. As the inorganic phase difference compensation elements, there have been proposed (1) a phase difference compensation element provided with a multi-layer thin film comprising a high refractive index thin film and a low refractive index thin film, which are laminated alternately with thicknesses smaller than light wavelengths, (as disclosed in, for example, Japanese Unexamined Patent Publication No. 2004-102200), and (2) a phase difference compensation element provided with a plurality of inorganic oblique incidence vacuum deposited films varying in direction of oblique evaporation (as disclosed in, for example, Japanese Unexamined Patent Publication No. 10 (1998)-081955.
With the phase difference compensation element (1) disclosed in, for example, Japanese Unexamined Patent Publication No. 2004-102200), the multi-layer thin film exhibits negative uniaxial birefringent characteristics and has the so-called negative C-plate characteristics. With the phase difference compensation element (1) disclosed in, for example, Japanese Unexamined Patent Publication No. 2004-102200), the phase difference compensating function (A) with respect to the birefringence of the oblique incident light is good, but the phase difference compensating function (B) with respect to the birefringence due to the liquid crystal molecules having been set in the hybrid orientated state is not sufficient.
The phase difference compensation element (2) disclosed in, for example, Japanese Unexamined Patent Publication No. 10(1998)-081955 has the laminate structure of the plurality of the inorganic oblique incidence vacuum deposited films having different birefringent characteristics. Therefore, it may be considered that, with the phase difference compensation element (2) disclosed in, for example, Japanese Unexamined Patent Publication No. 10 (1998)-081955, the phase difference compensating function (B) with respect to the birefringence due to the liquid crystal molecules having been set in the hybrid orientated state will be capable of being obtained. However, each of the inorganic oblique incidence vacuum deposited films constituted of a plurality of pillar-shaped crystals is apt to have an uneven surface. In cases where the plurality of the inorganic oblique incidence vacuum deposited films are overlaid one upon another, vacuum evaporation failures, such as agglomeration of the pillar-shaped crystals, are apt to occur with an inorganic oblique incidence vacuum deposited film, which is formed by later vacuum evaporation processing. Therefore, it is not always possible to achieve reliable formation of the films having desired optical characteristics. Also, if the agglomeration of the pillar-shaped crystals, or the like, occurs, there will be the risk that the film will suffer from cloudiness due to a light scattering phenomenon at the part at which the agglomeration has occurred, and that the optical characteristics, such as a transmittance, will become bad. In, for example, Japanese Unexamined Patent Publication No. 10 (1998)-081955, it is described that, with formation of frontal incidence vacuum deposited films located among the plurality of the inorganic oblique incidence vacuum deposited films, the occurrence of the vacuum evaporation failures of films formed by later vacuum evaporation processing may be suppressed, and the occurrence of cloudiness may thereby be suppressed. However, the formation of the frontal incidence vacuum deposited films located among the plurality of the inorganic oblique incidence vacuum deposited films is not appropriate from the view point of the number of production steps, the production cost, and the like. Also, in cases where unnecessary frontal incidence vacuum deposited films are located among the plurality of the inorganic oblique incidence vacuum deposited films, there will be the risk that the optical characteristics, such as the transmittance, will become bad.
In view of the above circumstances, the primary object of the present invention is to provide an inorganic phase difference compensation element, which has a good phase difference compensating function with respect to birefringent characteristics of liquid crystal molecules having been set in a hybrid orientated state, and which has good optical characteristics, such as phase difference compensating functions and a transmittance, good production easiness, and good production stability.
An other object of the present invention is to provide a liquid crystal device, in which the phase difference compensation element is employed.
A further object of the present invention is to provide a projection type display apparatus, in which the phase difference compensation element is employed.
The present invention particularly aims at furnishing the inorganic phase difference compensation element having the characteristics described above. However, the present invention is also applicable to an organic phase difference compensation element.